1. Field of the Invention
This invention relates broadly to surgery. More particularly, this invention relates to a bone fixation systems including plates and locking screws.
2. State of the Art
Fracture to the metaphyseal portion of a long bone can be difficult to treat. Improper treatment can result in deformity and long-term discomfort.
By way of example, a Colles' fracture is a fracture resulting from compressive forces being placed on the distal radius, and which causes backward or dorsal displacement of the distal fragment and radial deviation of the hand at the wrist. Often, a Colles' fracture will result in multiple bone fragments which are movable and out of alignment relative to each other. If not properly treated, such fractures may result in permanent wrist deformity and limited articulation of the wrist. It is therefore important to align the fracture and fixate the bones relative to each other so that proper healing may occur.
Alignment and fixation of a metaphyseal fracture (occurring at the extremity of a shaft of a long bone) are typically performed by one of several methods: casting, external fixation, pinning, and plating. Casting is non-invasive, but may not be able to maintain alignment of the fracture where many bone fragments exist. Therefore, as an alternative, external fixators may be used. External fixators utilize a method known as ligamentotaxis, which provides distraction forces across the joint and permits the fracture to be aligned based upon the tension placed on the surrounding ligaments. However, while external fixators can maintain the position of the wrist bones, it may nevertheless be difficult in certain fractures to first provide the bones in proper alignment. In addition, external fixators are often not suitable for fractures resulting in multiple bone fragments. Pinning with K-wires (Kirschner wires) is an invasive procedure whereby pins are positioned into the various fragments. This is a difficult and time consuming procedure that provides limited fixation if the bone is comminuted or osteoporotic. Plating utilizes a stabilizing metal plate that is typically placed against the dorsal side of a bone. Fixators extend from the plate into holes drilled in bone fragments are used to secure the fragments to the plate and thereby provide stabilized fixation of the fragments.
Commercially available are plates which use one of two types of fixators: i) unidirectional fixed angle locking screws (both smooth shaft screws and threaded shaft screws) that are fixed in a predetermined orientation relative to the plate with the head of the screws threadably engaging threaded holes in the plate, and ii) surgeon-directed or omnidirectional “locking” screws that can be fixed to the plate at any angle within a range of angles relative to the plate. Surgeon-directed locking screws are exemplified in SMARTLock™ screw system from Stryker Corporation, the Volar Bearing Plate™ from Trimed Inc., the VAL™ (volar angle locking) plate from US Implants, and the Viper™ plate with VALT™ (variable angle locking technology) from KMI Inc. The surgeon-directed “locking” screws require special structure and dedicated screw holes. All available plates with surgeon-directed locking screws have the hole axes for the screws all in a parallel orientation, and generally normal to the bone contacting surface of the plate. As the angle at which any surgeon-directed locking screw can be directed is limited relative to the hole axis (generally ±15°), the range of angles through which the screws can be inserted is greatly limited. As such, such systems often suffer from an inability to properly approach the desired anatomical structure with a fixator.
In addition, some plates permit the use of, or only use, non-locking screws in which there is no direct engagement between the head of the screw and the plate, but the screw shaft engages the bone and the plate and bone are held and relationship via compression created by driving the screw. Thus, in treating a particular bone fracture, an orthopedic surgeon is required to select one of these types of plate systems and the appropriate type of screws.
It is believed that a fixed angle locking screw, as opposed to a non-locking screw, provides advantage over the non-locking screw in that increased stability to the fracture is provided. In addition, compression which may be disadvantageous for many fractures is avoided.
There may be instances where improved bone stabilization and fixation can be accomplished utilizing both unidirectional and surgeon-directed locking screws. These features would allow the surgeon to better tailor the application of the plate system to the specific nature of the bone fracture suffered by the individual patient. However, no available system provides such capability.